https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import org.checkerframework.checker.nullness.qual.Nullable;


Legacy version of java.util.function.Predicate. Determines a true or false value for a given input. 
As this interface extends java.util.function.Predicate, an instance of this type may be used as a Predicate directly. To use a java.util.function.Predicate where a com.google.common.base.Predicate is expected, use the method reference 
predicate::test. 
This interface is now a legacy type. Use java.util.function.Predicate (or the appropriate primitive specialization such as IntPredicate) instead whenever possible. Otherwise, at least reduce explicit dependencies on this type by using lambda expressions
or method references instead of classes, leaving your code easier to migrate in the future.

The Predicates class provides common predicates and related utilities. 
See the Guava User Guide article on the use of Predicate.

Author:Kevin Bourrillion
Since:2.0
/**
 * Legacy version of {@link java.util.function.Predicate java.util.function.Predicate}. Determines a
 * true or false value for a given input.
 *
 * <p>As this interface extends {@code java.util.function.Predicate}, an instance of this type may
 * be used as a {@code Predicate} directly. To use a {@code java.util.function.Predicate} where a
 * {@code com.google.common.base.Predicate} is expected, use the method reference {@code
 * predicate::test}.
 *
 * <p>This interface is now a legacy type. Use {@code java.util.function.Predicate} (or the
 * appropriate primitive specialization such as {@code IntPredicate}) instead whenever possible.
 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions
 * or method references instead of classes, leaving your code easier to migrate in the future.
 *
 * <p>The {@link Predicates} class provides common predicates and related utilities.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Predicate}</a>.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@FunctionalInterface
@GwtCompatible
public interface Predicate<T> extends java.util.function.Predicate<T> {
  
Returns the result of applying this predicate to input (Java 8 users, see notes in the class documentation above). This method is generally expected, but not absolutely
required, to have the following properties:

    
  
  • Its execution does not cause any observable side effects.
  
  • The computation is consistent with equals; that is, 
      Objects.equal(a, b) implies that predicate.apply(a) ==
      predicate.apply(b)). 


Throws:
/**
   * Returns the result of applying this predicate to {@code input} (Java 8 users, see notes in the
   * class documentation above). This method is <i>generally expected</i>, but not absolutely
   * required, to have the following properties:
   *
   * <ul>
   *   <li>Its execution does not cause any observable side effects.
   *   <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal
   *       Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) ==
   *       predicate.apply(b))}.
   * </ul>
   *
   * @throws NullPointerException if {@code input} is null and this predicate does not accept null
   *     arguments
   */
  @CanIgnoreReturnValue
  boolean apply(@Nullable T input);

  
Indicates whether another object is equal to this predicate.

Most implementations will have no reason to override the behavior of Object.equals. However, an implementation may also choose to return true whenever object is a Predicate that it considers interchangeable with this one. "Interchangeable"
typically means that this.apply(t) == that.apply(t) for all t of type T). Note that a false result from this method does not imply that the predicates are known not to be interchangeable.

/**
   * Indicates whether another object is equal to this predicate.
   *
   * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}.
   * However, an implementation may also choose to return {@code true} whenever {@code object} is a
   * {@link Predicate} that it considers <i>interchangeable</i> with this one. "Interchangeable"
   * <i>typically</i> means that {@code this.apply(t) == that.apply(t)} for all {@code t} of type
   * {@code T}). Note that a {@code false} result from this method does not imply that the
   * predicates are known <i>not</i> to be interchangeable.
   */
  @Override
  boolean equals(@Nullable Object object);

  @Override
  default boolean test(@Nullable T input) {
    return apply(input);
  }
}